Generally, a coupling device includes an immovable socket (female coupler) and a movable plug (male coupler) both of which are arranged on an identical axis line. In the coupling device, the plug is inserted into the socket, providing a liquid-tight coupled state between the plug and the socket.
If such a coupling device has a relatively-small diameter, no problems occur when an operator connects the plug to the socket manually. On the contrary, if the coupling device has a relatively-large diameter, then it becomes difficult for an operator to push the plug into the innermost part of the socket in order to complete the connection, since such an operation requires a large amount of force from the operator.
In a coupling device disclosed in Japanese Registered Patent Publication No. 3349958, a plug is first pushed into a socket to some degree by an operator. In succession, through the use of pneumatic pressure, the plug is moved up to an advancing end where it is finally connected to the socket. Thus, according to the technique disclosed in Japanese Registered Patent Publication No. 3349958, even if the coupling device has a relatively-large diameter, the plug and the socket can be connected to each other relatively easily.
However, if supplying fluid (especially, liquid) after connecting the coupling device of a relatively-large diameter, a situation may occur in which the plug may become curved from a joint portion between the plug and the socket due to weight of the fluid. Particularly, in the case of supplying fluid at a relatively-large flow rate, not only does the plug oscillate thereby making it difficult to stably supply fluid, but also the joint portion between the plug and the socket may become damaged. In addition, when supplying multiple chemical liquids, problem arises in which an improper connection is made to the coupling device.
Under the above-mentioned situation, an object of the present invention is to provide a fluid-transfer coupling device that can supply fluid stably even when using the coupling device with a relatively-large diameter. Another object of the present invention is to supply a chemical liquid safely without causing such an improper connection in the coupling device.